The Wandering Gene and the Indian Princess: Race, Religion, and DNA
By Jeff Wheelwright
W.W. Norton and Company, 260 pages, $26.95
A diagnosis of breast cancer presents a lot of questions. Should you start with chemotherapy, or opt for surgery right away? Do you remove the tumor alone, or the entire breast? What about prophylactic surgery to remove the other healthy breast before the next tumor strikes?
Such questions can be daunting for any woman in the face of a life-threatening illness. But what if the questions raised by such a tumor go beyond how to control the disease? What if the cancer also fundamentally challenges the notions of your race, religion and personal identity?
Such was the case for a small group of Catholic Hispanos living in the San Luis Valley of southern Colorado. In addition to coming to grips with a hereditary form of breast cancer plaguing their community, this population of Spanish and Native American descent had to deal with their DNA, and a peculiar mutation that pointed unexpectedly to an ancient Jewish heritage.
That genetic defect goes by the name BRCA1.185delAG, so-called because of a deletion (del) of the chemicals adenine (A) and guanine (G) at site 185 of the DNA encoding the BRCA1 gene. It’s known, with dread, as the BRCA (pronounced “bracka”) mutation, and a woman with it has a greater than 50% chance of developing breast or ovarian cancer over her lifetime.
The 185delAG mutation arose some two millennia ago among the Hebrew tribes living in the Middle East and spread through their gene pool, rising in frequency. Currently there are two working hypotheses for this higher prevalence: first, that it rose in frequency by chance alone, because of the Jews’ small gene pool; second, natural selection caused the gene to rise. A recent study, published in the journal Biology Letters, suggests that having the mutant BRCA mutation may have boosted fertility in the days before birth control and that the evolutionary fitness of the gene was largely unaffected by its fatal consequences in later life. Whichever is the case, the mutation now affects about one in 100 people of Ashkenazi descent and, intriguingly, some isolated non-Jewish populations of Spanish descent, too.
About a decade ago, scientists began noticing the deletion of those two letters of DNA in several non-Jewish communities, including a Spanish Gypsy population, a Chilean family and Hispanic groups living in the Los Angeles area. All these people identified as Spanish or Latin American and had no knowledge of any Jewish ancestry. But DNA revealed what culture and history had lost.
Scientists typically refer to 185delAG as an “Ashkenazi” mutation, thanks to the gene’s most prominent carrier population today. But considering that Iraqi and Moroccan Jews carry the mutation at noticeable frequencies, chances are that the Sephardim of the Iberian Peninsula harbored the genetic red flag, as well.